The overall objective of this project is to elucidate the molecular mechanisms involved in the regulation of the growth and function of adrenocortical cells. During the past year, we succeeded in detecting and characterizing the physiologically relevant receptors for ACTH on rat adrenocortical cells for the first time. We also prepared a well-characterized photoreactive derivative of the hormone and used it to identify the ACTH receptor on adrenocortical cells. In addition, the photoreactive peptide was employed to identify the site of interaction between ACTH and serum albumin, which may be physiologically important in the transport of the hormone in incubation.